When making a Cat5 straight thru cable, going between a PC and a switch/hub, what color codes do I use for the RJ45 connectors? I have two long runs, probably 75 feet that aren't working. I'm using w/orange, orange..w/blue, blue..w/green, green and w/brown, brown. This may sound like a dumb question, but why do the colors matter as long as both ends are the same.

I get a link light on the NIC and the switch/hub but I can't do anything on the network.

You can use either standard color code, or invent you own, if desired. I use the 568A color code and it is the “preferred standard.” The colors do not matter, but the choice of wires does. Simply making both ends the same is not sufficient. The Ethernet interface uses four of the eight pins in an RJ-45 plug. Each end of an Ethernet cable connects to a transmitter and a receiver. A transmitter uses two pins and a receiver uses two pins. The two pins (+ and -) on the transmitter have to be connected to the corresponding pins (+ and -) of the receiver at the other end by wires in the SAME twisted pair and vice versa. A transmitter is not connected to a receiver by one wire from one pair and a second wire from a DIFFERENT pair. As the pins that are used, 1, 2, 3, and 6, are not sequential, one cannot simply match ends in a convenient manner and properly connect a transmitter to a receiver with wires from the SAME twisted pair. If this description seems a bit complicated or fuzzy, pictures can be found here: http://duxcw.com/digest/Howto/network/cable/cable5.htm. Larry

Q. Why would the Link (or LNK) LEDs be on solid, if there is a faulty cable connecting two Ethernet devices?

A. Solid Link LEDs usually indicate a good network connection between two network adapters connected by a crossover cable or between a PC and hub or switch connected by straight-thru cable, but not always...

10BASET and 100BASE-TX Ethernet interfaces have two transmit pins (+ and -) and two receive pins (+ and -). The rest of the pins are unused. Transmit + pins must be connected to receive + pins, etc.

Solid LINK (or LNK) LEDs on two 10/100 Ethernet devices (network interface card--NIC, hub, switch, etc.) that are connected together indicates that the two transmit pins are connected to the correct receive pins. It does not, however, guarantee that the cable is made properly, is made with the correct cable and connectors, and that will reliably transmit data. For example, the Ethernet standard specifies that the transmit pins be connected to corresponding receive pins with wires from the same twisted pair. It is certainly possible to connect a set of pins using one wire from one pair and another wire from a different pair. The reason it is possible to get solid LINK LEDs and unreliable data transfers is that link determination is made with a link integrity test pulse which is transmitted at a much slower rate than the actual Ethernet signals that transfer data. Broken, disconnected, improperly terminated (coax), or miswired cables are responsible for over 70% of all LAN problems.